This invention concerns air conditioning systems and more particularly a conditioning system adapted to carry out chemical or liquid solution absorption of the air moisture to achieve dehumidification.
In copending applications, Ser. No. 882,345, filed Mar. 1, 1978 and Ser. No. 887,156, filed Mar. 16, 1978, air supply systems for paint spray booths are described. Such systems are utilized in order to condition ambient air prior to being circulated through a paint spray booth. Paint spraying operations are carried out on products such as automotive car bodies and similar production items, and in order to provide healthful working conditions, a fresh supply of incoming air is continuously either cooled or heated, dehumidified or humidified, and exhausted to the atmosphere after passing through the booth.
As described in these patent applications, a critical aspect of the air supply system is the maintenance, during winter and summer, of the relative humidity of the air supply for paint spraying water based paints.
Typically, during summertime operation, the relative humidity must be reduced from ambient levels since the relative humidity is usually well above the relative humidity level required to be maintained (50%). Particularly, this is so since the air temperature is usually reduced by the conditioning process, raising the relative humidity.
Conversely, during wintertime operation, the relatively cold, dry outside air upon being heated must be adjusted in humidity so as to raise the relative humidity of the incoming air supplied to the paint spray booth.
Various conventional methods have been utilized in the past in order to carry out the dehumidification.
In one method, the air is chilled to a dew point temperature which corresponds to the correct relative humidity, which dew point temperature is well below the dry bulb temperature of the air supplied to the paint spray booth, and then reheated to the appropriate dry bulb temperature to thus achieve the proper relative humidity.
Another system which has been utilized is the so-called chemical or liquid absorption system. This system relies on the use of a chemical salt solution such as lithium chloride or other suitable materials such as ethylene glycol in a water solution. Such solutions exhibit the characteristic of a reduced vapor pressure of the water above such solutions as compared to pure water. Thus, if the existing vapor pressure of the water vapor in the incoming air is above such reduced vapor pressure, the result is that the ambient water vapor is condensed into the solution.
In practice, the solution is sprayed into the incoming air and collected in a collection pan and recirculated to be resprayed in the system. The moisture in the air being condensed into the solution, the latent heat of condensation is absorbed into the solution. In addition, the incoming air is commonly at a higher temperature than the absorption solution and the solution is therefore heated by direct heat transfer between the air and the sprayed solution. Finally, there is also released a so-called heat of dilution as the condensed moisture passes into the solution.
The phenomenon of liquid absorption, depending on the reduced vapor pressure exhibited by the solution, is only effective when the temperature of the solution is sufficiently low since with increasing temperatures of the solution, the vapor pressure would increase to a point whereat liquid absorption would no longer take place or would take place at inadequate rates.
Thus, as the heat from the various sources is absorbed by the solution, the temperature of the solution is increased and must be reduced, i.e., heat extracted or rejected in order to maintain the effectiveness of the process.
Conventional systems commonly sought to eliminate the heat generated by the use of evaporative cooling towers. While this is generally satisfactory, the use of evaporative cooling towers entails considerable capital expense and in addition places relatively severe constraints on the temperature to which the solution may be reduced. That is, the evaporative cooling is limited in the temperature to which the water may be reduced, of the order of 87.degree. F. for a design summer peak condition of 96.degree. F. ambient.
In addition to the solution cooling requirements, the effectiveness of the solution also depends on the concentration of the solution. As the moisture passes into the solution, the resultant dilution reduces the effectiveness of the process, requiring the regeneration or reconcentration of the solution as the process proceeds. The usual method for reconcentrating the solution is to heat the same and pass ambient air over a spray of the dilute solution, the relatively elevated temperature levels of the solution allowing the ambient air to carry out the moisture, thus achieving the reconcentration.
Since typically, the ambient air is at relatively high humidity levels, the solution must be heated to a relatively high temperature, requiring the expenditure of considerable heat. Such heat is supplied by an external heat source such as a steam boiler. This thus requires a supply of steam and also entails the expenditure of energy which is growing more and more costly and is of reduced availability in recent times.
While some systems employ a heat exchange between the absorption liquid in the primary circuit and the regenerator circuit, the process still requires considerable cooling and heating capability.
It is accordingly the object of the present invention to provide for a system and method for liquid absorption humidity conditioning of an air supply in which the need for equipment and energy is greatly reduced over that required in conventional systems.